Angewandte
Chemie
quantitatively recovered when one equivalent (relative to Ni)
of HCl (in dioxane) was added. However, the addition of
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HBF (in diethyl ether) led to the complete consumption of
4
VCP 1, but neither diene nor cyclopentene was detected. (The
product of this reaction has been elusive thus far.) Never-
theless, these results suggest that the VCP isomerizations
[
0
were catalyzed by an Ni species and do not involve nickel
hydrides.
2324 – 2326; d) J. P. Dinnocenzo, D. A. Conlon, Tetrahedron
Although a number of nitrogen-heterocyclic carbenes are
indefinitely stable under an inert atmosphere, they can be
easily generated in situ from the appropriate precursor salt
Lett. 1995, 36, 7415 – 7418; e) K. Miura, K. Fugami, K. Oshima,
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[
13]
and base. Such a method has been used in a variety of
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[
14]
metal-mediated reactions, including olefin metathesis, the
624.
[
15]
Suzuki–Miyaura reaction, the Buchwald–Hartwig amina-
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b) Y. Morizawa, K. Oshima, H. Nozaki, Tetrahedron Lett. 1982,
[
16]
[17]
tion, and the Kumada–Corriu reaction. Similarly, VCP 1
23, 2871 – 2874; c) M. Hayashi, T. Ohmatsu, Y.-P. Meng, K.
was subjected to catalytic amounts of [Ni(cod) ](5 mol%),
2
Saigo, Angew. Chem. 1998, 110, 877 – 879; Angew. Chem. Int. Ed.
IPrBF (10 mol%), and KOtBu (10 mol%) in pentane. A
4
1998, 37, 837 – 839; d) H. M. Davies, B. Hu, J. Org. Chem. 1992,
quantitative yield of cyclopentene product 2 was observed by
gas chromatography after only 12 h at room temperature.
In conclusion, we have developed a mild and efficient
protocol for the preparation of cyclopentenes from the
isomerization of vinyl cyclopropanes. The reaction employs
57, 3186 – 3190; e) T. Hudlicky, F. J. Koszyk, T. M. Kutchan, J. P.
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0
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catalytic amounts of Ni and a nitrogen-heterocyclic carbene
ligand. Most importantly, activated VCPs are not required for
efficient transformation. We are currently working toward
expanding the substrate scope, enhancing the catalyst per-
formance, and understanding the mechanism of this reaction.
[
[
8]a) A. B. Charette, A. Giroux, J. Org. Chem. 1996, 61, 8718 –
8719; b) R. E. Taylor, F. C. Engelhardt, M. J. Schmitt, H. Yuan,
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Experimental Section
[
9]For an example of using Ni/NHC complexes to mediate coupling
of 1,3-dienes with aldehydes, see: Y. Sato, R. Sawaki, M. Mori,
Organometallics 2001, 20, 5510 – 5512.
Representative procedure: In a dry-box, VCP 1 (200 mg, 1.2 mmol)
was added to an oven-dried screw-cap vial equipped with a magnetic
stirrer bar and was subsequently dissolved in pentane (1.5 mL).
Alternatively, the reaction may be performed outside of a drybox by
adding VCP 1 and dry, degassed pentane through a syringe to an
oven-dried flask (which has previously been evacuated and filled with
[
[
[
[
10]The nature of the active Ni catalyst is currently under
investigation.
11]P. A. Pinke, R. D. Stauffer, R. G. Miller, J. Am. Chem. Soc. 1974,
9
6, 4229 – 4234.
12]D. E. Berning, B. C. Noll, D. L. DuBois, J. Am. Chem. Soc. 1999,
21, 11432 – 11447.
N ) equipped with a septum, stirrer bar, and gas-adapter. A solution
2
of [Ni(cod) ](3 mg, 0.01 mmol) and IPr (8 mg, 0.02 mmol) in pentane
2
1
(0.5 mL) that had previously equilabrated for 12 h was then added
13]The tetrafluoroborate salts of 1,3-bis-(2,6-diisopropylphenyl)-
and the reaction vessel was sealed appropriately. The resulting dark
greenish-black solution was then stirred at room temperature until
the starting material was completely consumed (as determined by
GC). The products were then purified by chromatography on silica
gel (with pentane as the eluent).
imidazol-2-ylidene (IPrBF ) and 1,3-bis-(1,3,5-trimethylphenyl)-
4
imidazol-2-ylidene (IMesBF ) are commercially available from
4
Strem Chemicals, Inc., Newburyport, MA.
[
14]a) J. P. Morgan, R. H. Grubbs, Org. Lett. 2000, 2, 3153 – 3155;
b) J. Louie, R. H. Grubbs, Angew. Chem. 2001, 113, 253 – 255;
Angew. Chem. Int. Ed. 2001, 40, 247 – 249.
Further experimental details are available in the Supporting
Information.
[
15]C. Zhang, J. Huang, M. L. Trudell, S. P. Nolan, J. Org. Chem.
1
999, 64, 3804 – 3805.
16]a) H. Huang, G. Grasa, S. P. Nolan, Org. Lett. 1999, 1, 1307 –
309; b) S. R. Stauffer, S. Lee, J. R. Stambuli, S. I. Hauck, J. F.
Hartwig, Org. Lett. 2000, 2, 1423 – 1426.
[17]H. Huang, S. P. Nolan, J. Am. Chem. Soc. 1999, 121, 9889 – 9890.
Received: December 5, 2003 [Z53469]
[
1
Keywords: carbene ligands · cyclopentenes · isomerization ·
nickel · rearrangement
.
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ꢀ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2279